This invention relates to shaft motion sensing in a reciprocating internal combustion engine, and more particularly to a method of diagnosing proper operation of a shaft sensor.
Control systems for reciprocating internal combustion engines rely extensively on input signals obtained from various types of sensors. One of the most important inputs is obtained from a sensor (usually a magnetic flux responsive sensor) positioned in proximity to the teeth of a rotary wheel such the engine flywheel gear for providing an indication of crankshaft movement; typically, this input is used by the engine controller to determine both engine crankshaft position (rotary orientation) and speed for purposes of properly regulating control parameters such as spark timing and fuel delivery. Accordingly, it is highly desirable to promptly diagnose crankshaft sensor failures so that alternate or default control strategies may be initiated. Since the use of redundant sensors is usually cost prohibitive, failure of the crankshaft sensor is sometimes diagnosed on the basis of an input provided by a camshaft sensor, as the camshaft is mechanically coupled to the crankshaft. However, not all engine control systems include a camshaft sensor. Accordingly, what is desired is a method of diagnosing crankshaft sensor failures based on sensor information that is routinely available in an engine control system.
The present invention is directed to an improved method of diagnosing shaft sensor failure in a reciprocating internal combustion engine in which engine rotation is verified by sensor information responsive to dynamic variation in engine air intake that occurs during engine rotation, and failure of the shaft sensor is diagnosed when the dynamic variation in engine air intake is detected in the absence of a shaft sensor signal. The sensor information used to detect the dynamic variation in intake air may be obtained from either a mass air flow sensor disposed in a throttle body of the engine, or from a pressure sensor disposed in an intake manifold of the engine, and virtually all current engine control systems utilize at least one of these sensors. Three different methodologies for detecting dynamic variation of the air intake signal are described. According to a first embodiment, the variation is detected by recognizing rising and falling segments of the signal waveform. In a second embodiment, the variation is detected by computing a relative manifold pressure and comparing it to predetermined maximum and minimum values. In a third embodiment, the variation is recognized by using a derivative of the signal to recognize the waveform inflection points.